In my hands MRC-5 do not get transfected with Lipo2000, but with Lipo3000 I got nice efficiency with plasmids! BJ are harder to transfect, I used lentiviruses, but after few passages they stopped to grow!
The medium you are creating the single cell suspensio for reverse transfection or forward transfection (seed the cells the day before transfection) should be free of antibiotics, these will interfere with the lipoplexes and reduce your transfection efficiency. Use the normal cultivation medium without antibiotics, the cells will not be influenced. Add the antibiotic one day after the transfection when it is necessary.